Abstract Noise-induced hearing loss (NIHL) is becoming increasingly common in industrialized countries, stemming from both workplace noise exposure and leisure activities. Corresponding with its functional deficit, loss of outer hair cells (OHCs) and synaptic ribbons are the primary inner ear pathology. Although a variety of biochemical and pathological events associated with OHC death have been reported, there is currently no established clinical therapy for the prevention or treatment of NIHL, owing largely to the lack of a comprehensive understanding of the precise molecular mechanisms and signaling pathways mediating OHC injury and loss of synaptic ribbons in response to noise exposure. The long-term goal of this research is to understand the molecular mechanisms that result in NIHL and to elucidate novel and rational pharmacological or molecular/genetic therapeutic interventions to ameliorate or prevent NIHL. We have previously reported that traumatic noise transiently depletes cellular energy reserves and increases levels of the energy sensor p- AMPK? in OHCs. Our exciting new preliminary results show an increased amount of mitochondrial calcium uniporter (MCU) and a decreased amount of the mitochondrial sodium calcium exchanger (NCLX) proteins in OHCs after noise exposure. The magnitude of these changes is positively correlated with noise intensity. Furthermore, such changes occur secondarily to noise-induced energy depletion and influx of calcium. Based on these data, the hypothesis is presented that the noise-induced increase of MCU moves calcium into mitochondria while the depression of NCLX reduces the extrusion of calcium out of mitochondria, actions that together create mitochondrial calcium overload. We will address this hypothesis using a comprehensive experimental approach employing both in-vivo studies with adult mice and a novel in-vitro model of energy depletion in an inner ear cell line model for testing specific aspects of the molecular mechanisms of NIHL. We also will use knockout mice, siRNA, gene therapy, and pharmacological compounds to block selected pathways that promote mitochondrial calcium overload in an attempt to achieve synergistic protection against NIHL. The results of this project will lead to new insights into mechanisms of NIHL and may direct the design of novel interventions for the prevention of NIHL benefiting the quality of life of individuals and reducing healthcare costs. In addition, the data generated in this proposal will make a significant contribution to our understanding of a broad range of inner ear disorders, since similarities have already been noted in the molecular events associated with noise-induced, drug-induced, and age-related hearing loss.